The present invention relates to methods and systems for controlling a steering system, and more particularly to methods and system for determining a damping and controlling the steering system based on the damping.
In a hydraulic assisted power steering system, a pump provides a constant flow (Qs) to an open center valve assembly that controls the level of assist pressure to the system based on the driver torque applied to the valve. The assist is communicated to the hydraulic cylinder through a pair of cylinder lines. This creates a differential pressure (PH-PL) across a piston attached to a rack to generate a force (F) at the tie rods to steer the vehicle.
In the static condition, the supply flow (QS) will divide through the valve assembly across the metering edges of the valve to achieve equilibrium, as shown in FIG. 1A. When the rack moves, however, a flow (QL) is required in the cylinder lines to accommodate the volume changes in the cylinder as shown in FIG. 1B. This in turn reduces the flow across the metering edges in the valve, which changes the amount of assist generated in the system. This has the effect of providing damping in the hydraulic system.
Accordingly, it is desirable to provide control methods and systems for electric power steering systems that provide and/or mimic damping in a similar manner as the hydraulic systems.